I would say that the bigger difference isn’t so much about the leadership style as it is that Cuomo won. Suppose that the New York State Senate operated according to the rules of the United States Senate and a bill failed unless it secured a 60 percent supermajority. What would people be saying about Andrew Cuomo now? Well, it seems to me that many people would be castigating his failed leadership.

It’s unlikely, certainly, that Mr. Cuomo would have persuaded the New York Senate to adopt a same-sex marriage bill if a 60 percent supermajority had been required. (That would have necessitated 38 votes rather than the 33 the bill actually received.) But I’m not sure that really gets to the heart of my argument.

My point, rather, is that Mr. Cuomo achieved a significant and perhaps improbable victory even relative to the more modest constraints that he actually faced.

How do we “know” this? There are two pretty obvious reasons. First, a highly similar bill failed badly in the New York Senate just 18 months ago, receiving only 24 votes. And during the interim period, Republicans won control of the body from Democrats. To be sure, there were also other factors helping Mr. Cuomo — most notably, that public opinion is shifting fairly rapidly toward acceptance of same-sex marriage. But the comparison — 33 votes against 24 — is nevertheless impressive.

We can also compare New York to other states. On Friday, it became the eighth state to adopt a gender-neutral marriage law (counting California and Maine, where the laws have since been repealed). But among the other seven states, all but New Hampshire and Maine did so as a direct or indirect result of court intervention. (New Hampshire and Maine are also somewhat less religious than New York, and religious affiliation is the most important predictor of public support for same-sex marriage.) That Mr. Cuomo was able to pass a bill while, for example, the governors of Rhode Island and Washington and Hawaii and Illinois and Maryland have not been able to pass one — that’s another sign that he’s achieved something significant.

Neither of these comparisons are perfect — but they’re much closer than you’re usually going to get in the real world to a controlled scientific experiment. We don’t need to delve too deeply into the netherworld of counter-factuals to conclude that Mr. Cuomo’s leadership likely made some difference.

Mr. Yglesias’ disagreement, I know, is not really about my evaluation of Mr. Cuomo, but instead about the comparison I’ve made to Mr. Obama, who he suggests faces far more constraints than Mr. Cuomo does:

[If] the US Senate operated on a 50 vote rule, then both the Affordable Care Act and the Dodd-Frank bill would have gone further in advancing progressive priorities, there would have been more economic stimulus in the 111th Congress, the DREAM Act would have passed, and it’s conceivable that some kind of nationwide carbon pricing scheme would be in place.

Okay, now I am going to need to engage in a hypothetical.

Suppose that Mr. Cuomo had expressed his desire to pass a marriage bill on the campaign trail, as he in fact did last year. But when he got to Albany, he decided to punt on the issue.

What would Mr. Cuomo have said? He would have mentioned that Republicans had taken over control of the Senate, something he had not necessarily anticipated. He would have reminded voters that the bill had been well short of passage the last time around. He might suggest that he thought he could round up a few more votes — but neither he nor the Republicans saw much point in bringing up a bill that was probably going to fail. He might tell his supporters that the prospects looked pretty bright for 2013.

It seems to me that this would have been an entirely reasonable-sounding argument. When there were some annoyed posts from liberal and gay and lesbian bloggers expressing disappointment with Mr. Cuomo’s decision, perhaps someone like Mr. Yglesias would have weighed in by saying that politics is the art of the possible — and sorry, but it just wasn’t going to be possible to get a gay marriage bill through a Republican majority.

The point is that it isn’t always such a simple matter to know exactly what is possible and what isn’t. Passing a same-sex marriage through the New York Senate might have seemed impossible this year — until Mr. Cuomo actually did it.

This is something we ought to keep in mind when we consider the case of Mr. Obama. We might say, for example, that Mr. Obama didn’t pass the DREAM Act because he didn’t have the votes for it in an environment where a Republican filibuster was likely. Literally speaking, this is true: if you don’t have the votes, you can’t pass the bill! But it also doesn’t really tell you anything — it’s a tautological statement equivalent to saying that the Cowboys won the football game because they scored more points than the Redskins.

The question, rather, is why Mr. Obama didn’t have the votes for something like the DREAM Act. Or more to the point: are there alternate strategies that Mr. Obama might have pursued under which he would have had the votes? (Even the filibuster, although it has become a significant part of the Senate’s culture, isn’t written into the Constitution: there are options to overcome it. They may be neither feasible nor wise options, but there are options.)

Of course, now we do get into questions that are hard — check that, impossible — to answer. We’ve taken an irrevocable detour into hypotheticaland. Unlike Mr. Cuomo, Mr. Obama did not have a Democratic predecessor. Cross-national comparisons are problematic, because most other Western industrialized nations have parliamentary systems. There’s not any “scientific” way to say how effective Mr. Obama has been in achieving his agenda, especially so early in his term.

But there are two types of arguments that I tend to be skeptical of. One is that the world that actually resulted (for example Mr. Obama’s winning passage of a health care bill but not a climate bill) is necessarily the best possible world. This is one (perhaps slightly unfair) way to read Mr. Ygelsias’ post — that Mr. Obama accomplished about as much as could reasonably be expected under the circumstances.

The other is the argument that an alternate strategy would necessarily have produced a better outcome. These arguments take the form of: if Mr. Obama had done X rather than Y, he could have accomplished P rather than Q, or maybe even both P and Q! (The possibility that the strategy might have failed and that neither P nor Q would have been achieved is usually not considered.)

Both types of arguments are hard to prove — or to disprove. That doesn’t mean I begrudge people for making them. But they ought to be stated as speculative, rather than as self-evident truths.

This fault is easy to detect when the argument is explicitly based on a hypothetical. But Mr. Yglesias’ argument implicitly suffers from the same fault: it takes for granted that the constraints Mr. Obama apparently faced (like the lack of Republican support for many of his bills) were not in some way of his own making. Even if Mr. Yglesias’ point gets it more right than wrong — as I suspect it does, since the Congress is in the midst of a long-term trend toward more partisanship — there may have been some wiggle room around the margins.

Back in the real world, here’s one thing I think we can say about Mr. Obama: he’s chosen his fights carefully. The way that we “know” this is to look at Mr. Obama’s failures rather than his successes.

There are essentially two ways that a president can fail when he needs the cooperation of Congress, one being that an issue fails to pass despite the president investing a significant amount of political capital in it, and the second being that he punts on the issue and doesn’t devote much time to it at all.

Mr. Obama has had very few failures of the first kind — as, for example, Bill Clinton did on his health care bill, or George W. Bush did in his efforts to privatize Social Security. Generally, when Mr. Obama has invested himself in a bill, he has secured passage of it.

On the other hand, there are a lot of fights that Mr. Obama has avoided. At least insofar as is evident from his public statements, he didn’t make a major push for climate change legislation, or for an immigration bill like the DREAM Act, or for a second stimulus. He hasn’t taken as confrontational a posture as he might have with Republicans on the debt ceiling.

The point is not that this is the right strategy or the wrong strategy. It might well have been the right strategy — I don’t come to a conclusion about that. But I do think it’s fair to characterize it as a risk-averse strategy. And that, at the core, is what bothers some liberals about Mr. Obama’s approach to the presidency. Fairly or not, they want him to push the envelope more than he has and to take a few more chances — to expand the realm of the possible, as Mr. Cuomo seems to have done in New York.

Nate Silver is the founder and editor in chief of FiveThirtyEight. @natesilver538

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